Difficulty: Easy
Correct Answer: Methane
Explanation:
Introduction / Context:
Gobar gas, also called biogas, is an important form of renewable energy in rural areas. It is produced by the anaerobic decomposition of organic matter, often cattle dung mixed with water, in a biogas plant. Understanding the main component of gobar gas helps explain why it can be used as a fuel for cooking, lighting, and small scale power generation. This question tests basic environmental science and chemistry knowledge related to rural energy technologies and sustainable development.
Given Data / Assumptions:
Concept / Approach:
In a typical biogas plant, microorganisms break down organic material in the absence of oxygen. During this anaerobic digestion process, complex organic compounds are converted into simpler molecules, producing a gas mixture known as biogas. The main component of this gas is methane, which is a combustible fuel. Biogas also contains carbon dioxide and small amounts of other gases such as hydrogen sulfide and water vapour. However, methane usually makes up more than half of the mixture and is responsible for its energy content. This is why biogas can be burned for cooking and heating in a similar way to natural gas, which is also methane rich.
Step-by-Step Solution:
1. Recognize that gobar gas is a form of biogas generated from organic waste like cattle dung under anaerobic conditions.2. Recall that the main purpose of producing gobar gas is to obtain a burnable fuel for household uses.3. The gas that burns easily and is the primary fuel component in biogas is methane.4. Biogas does contain carbon dioxide and traces of other gases, but these components do not contribute as much to its fuel value.5. Ethane and hydrogen may be present in negligible amounts or not at all in typical rural biogas plants.6. Therefore, the chief gaseous constituent of gobar gas is methane.
Verification / Alternative check:
Descriptions of biogas composition in environmental science texts usually report methane concentrations of about 50 to 70 percent, with most of the remaining volume being carbon dioxide and only small amounts of other gases. The calorific value of biogas is directly linked to this methane content. Practical experiences in rural energy projects also confirm that biogas burns with a blue flame similar to that of liquefied petroleum gas or natural gas, indicating a methane based fuel. These facts clearly support methane as the main constituent of gobar gas.
Why Other Options Are Wrong:
Option B, carbon dioxide, is incorrect because although it is present in biogas, it is non combustible and does not provide fuel value, so it cannot be called the chief constituent in terms of energy. Option C, ethane, is a hydrocarbon found in some natural gas deposits, but it is not typically the main product of cattle dung based biogas digestion. Option D, hydrogen, can be a component in some gas mixtures but is present only in small amounts in standard gobar gas and is not the primary fuel component.
Common Pitfalls:
One common confusion is to assume that the largest volume component of any gas mixture must be carbon dioxide, because of its prominence in climate discussions. However, in biogas the key point is which gas provides fuel value. Another pitfall is mixing up different fuel gases such as methane, ethane, propane, and hydrogen. Remember that gobar gas and many natural gas resources are described as methane rich, and this association helps you quickly identify methane as the chief constituent in exam questions.
Final Answer:
The chief gaseous constituent of gobar gas or biogas produced from cattle dung is methane, which makes the gas mixture a useful fuel.
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